An ocellaris, with the limited space is my vote for a number of reasons;

a) they're narcissistic as hell, so you'll see them all the time
b) very hardy; my two have been with me six years at this point, suffering through my stupidity and experimention
c) won't bother corals--mine have hosted in a frogspawn for years
d) you can't beat the coloration
e) will eat anything
f) i haven't had one person walk past my nano tank without saying, "hey neat, a clown fish"

I also like the purple firefish, however, they are a bit reclusive.

Hope this helps.

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